8086 Microprocessor

Microprocessor

Program controlled semiconductor device (IC) which fetches (frommemory), decodes and executes instructions.

It is used as CPU (Central Processing Unit) in computers.

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Microprocessor

First GenerationBetween 1971 – 1973

PMOS technology, non compatible with TTL4 bit processors 16 pins

8 and 16 bit processors 40 pinsDue to limitations of pins, signals are

multiplexed

Second GenerationDuring 1973NMOS technology Faster speed, Higher density, Compatible with TTL4 / 8/ 16 bit processors 40 pinsAbility to address large memory spaces and I/O portsGreater number of levels of subroutine nestingBetter interrupt handling capabilities

Intel 8085 (8 bit processor)

Third GenerationDuring 1978

HMOS technology Faster speed, Higher packing density

16 bit processors 40/ 48/ 64 pinsEasier to program

Dynamically relatable programsProcessor has multiply/ divide arithmetic

hardwareMore powerful interrupt handling

capabilitiesFlexible I/O port addressing

Intel 8086 (16 bit processor)

Fourth GenerationDuring 1980sLow power version of HMOS technology (HCMOS)32 bit processorsPhysical memory space 224 bytes = 16 MbVirtual memory space 240 bytes = 1 TbFloating point hardwareSupports increased number of addressing modes

Intel 80386

Fifth Generation Pentium

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Features:•It requires a single +5V supply•It is a 16 bit processor•It can access a memory of 1MB(2^20)•It can generate 16 bit I/O address hence it can access2^16=65536 I/O ports•It is possible to perform bit, byte, word and blockoperations•The Intel 8086 is designed to operate in two modesnamely minimum mode and maximum mode•The Intel 8086 supports multiprogramming•The words will be stored ion two memory locations.If the first byte of word is at an even address, the8086 will read the entire word in one operation.If the first byte of word is at odd address, the 8086will read the first byte in one operation and thesecond byte in another operation

Architecture of 8086

• The architecture of 8086 includes

– Arithmetic Logic Unit (ALU)

– Flags

– General registers

– Instruction byte queue

– Segment registers

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EU & BIU

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General Register

Control Register

Segment Register

CPU Register Set

Data Register

Index Register

Pointer Register

AH AL

BH BL

CH CL

DH DL

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Stack Pointer (SP)

Base Pointer (BP)

Source Index (SI)

Destination Index (DI)

Code Segment (CS)

Data Segment (DS)

Extra Segment (ES)

Stack Segment (SS)

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Registers OperationAX Word multiplication and division, word I/O

AL Byte multiplication and division, Byte I/O, Translation, Decimal Arithmetic Operations

AH Byte multiplication and division

BP Enter, Leave 80186 or 80286 onwards

BX Translation and Base register

CX String Operation and Counter

CL Variable shift and rotate

DX Word multiplication and division

SP Stack Operation

SI & DI String Operation

Functional blocksMicroprocessor

Flag Register

Timing and control unit

Register array or internal memory

Instruction decoding unit

PC/ IP

ALU

Control Bus Address Bus

Data Bus

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Computational Unit;performs arithmetic andlogic operations

Various conditions of the results are stored as

status bits called flags in flag register

Internal storage of data

Generates theaddress of theinstructions to befetched from thememory and sendthrough addressbus to thememory

Decodes instructions; sendsinformation to the timing andcontrol unit

Generates control signals forinternal and externaloperations of themicroprocessor

Overview 8086 Microprocessor

First 16- bit processor released byINTEL in the year 1978

Originally HMOS, now manufacturedusing HMOS III technique

Approximately 29, 000 transistors, 40pin DIP, 5V supply

Does not have internal clock; externalasymmetric clock source with 33%duty cycle

20-bit address to access memory canaddress up to 220 = 1 megabytes ofmemory space.

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Pins and signals

Pins and Signals8086 Microprocessor

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Common signals

AD0-AD15 (Bidirectional)

Address/Data bus

Low order address bus; these aremultiplexed with data.

When AD lines are used to transmitmemory address the symbol A is usedinstead of AD, for example A0-A15.

When data are transmitted over AD linesthe symbol D is used in place of AD, forexample D0-D7, D8-D15 or D0-D15.

A16/S3, A17/S4, A18/S5, A19/S6

High order address bus. These aremultiplexed with status signals